The invention relates to a process for manufacturing high-density polyethylene and, more precisely, to a controlled process for polymerizing ethylene by separate injection of catalytic components.
When shaping high-density polyethylene by blow molding, it is essential that the polymer have a broad molecular weight distribution and a proportion of very high molecular weights as high as possible. When high-density polyethylene was manufactured according to to the high-pressure process, e.g. in British Pat. Nos. 1,441,115, 1,441,117 and 1,482,444, this problem was difficult to solve whatever catalytic components were used for the polymerization.
The use of complexing agents to modify molecular weight distribution is already known in the manufacture of high-density polyethylene according to the low pressure (less than 100 bars) and low temperature (less than 180.degree. C.) process, in which the complexing agent is injected into the reactor together with the other catalytic components. The technique of U.S. Pat. No. 3,929,754 is also known, according to which ethylene is polymerized at high temperature and under high pressure by means of a Ziegler-type catalyst comprising a titanium alcoholate and/or silicon oil. The art has not, however, solved the problems that this invention is concerned with.